Bot having high speed stability

ABSTRACT

An autonomous transport vehicle for transporting items in a storage and retrieval system is provided. The autonomous transport vehicle includes at least two drive wheels and a controller, where each drive wheel is independently driven and a drive wheel encoder is disposed adjacent each drive wheel. The controller, in communication with the drive wheel encoders, is configured to determine a kinematic state of the autonomous transport vehicle within the storage and retrieval system based on incremental data from the drive wheel encoders only and independent of drive wheel slippage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/326,447 filed on Dec. 15, 2011 and is a non-provisional of and claimsthe benefit of U.S. provisional patent application Ser. No. 61/423,359filed on Dec. 15, 2010, the disclosures of which are incorporated byreference herein in their entireties.

BACKGROUND

1. Field

The embodiments generally relate to storage and retrieval systems and,more particularly, to autonomous transports of the storage and retrievalsystems.

2. Brief Description of Related Developments

Warehouses for storing case units may generally comprise a series ofstorage racks that are accessible by transport devices such as, forexample, fork lifts, carts and elevators that are movable within aislesbetween or along the storage racks or by other lifting and transportingdevices. These transport devices may be automated or manually driven.Generally the items transported to/from and stored on the storage racksare contained in carriers, for example storage containers such as trays,totes or shipping cases, or on pallets.

When transporting the cases to and from the storage racks with automatedtransports it would be advantageous to be able to transport the cases athigh speeds using autonomous transport vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the disclosed embodimentsare explained in the following description, taken in connection with theaccompanying drawings, wherein:

FIG. 1 schematically illustrates an exemplary storage and retrievalsystem in accordance with the embodiments;

FIG. 2 illustrates a schematic plan view of an exemplary storage andretrieval system in accordance with the embodiments;

FIGS. 3A-3C illustrate schematic views of an exemplary autonomoustransport vehicle in accordance with the embodiments;

FIGS. 4A-4E illustrate storage shelves and an exemplary autonomoustransport vehicle in accordance with the embodiments;

FIG. 5 is a schematic illustration of a portion of the storage andretrieval system in accordance with the embodiments; and

FIGS. 6-8 are flow diagrams in accordance with aspects of theembodiments.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT(S)

FIG. 1 schematically illustrates an exemplary storage and retrievalsystem in accordance with the embodiments. Although the disclosedembodiments will be described with reference to the embodiments shown inthe drawings, it should be understood that the disclosed embodiments canbe embodied in many alternate forms. In addition, any suitable size,shape or type of elements or materials could be used.

In accordance with the embodiments the storage and retrieval system 100may operate in a retail distribution center or warehouse to, forexample, fulfill orders received from retail stores for case units(where case units as used herein means items not stored in trays, ontotes or on pallets, e.g. uncontained or items stored in trays, totes oron pallets). It is noted that the case units may include cases of items(e.g. case of soup cans, boxes of cereal, etc.) or individual items thatare adapted to be taken off of or placed on a pallet. In accordance withthe embodiments, shipping cases or case units (e.g. cartons, barrels,boxes, crates, jugs, totes, pallets or any other suitable device forholding case units) may have variable sizes and may be used to holditems in shipping and may be configured so they are capable of beingpalletized for shipping. It is noted that when, for example, bundles orpallets of case units arrive at the storage and retrieval system thecontent of each pallet may be uniform (e.g. each pallet holds apredetermined number of the same item—one pallet holds soup and anotherpallet holds cereal) and as pallets leave the storage and retrievalsystem the pallets may contain any suitable number and combination ofdifferent items (e.g. each pallet may hold different types of items—apallet holds a combination of soup and cereal). In the embodiments thestorage and retrieval system described herein may be applied to anyenvironment in which case units are stored and retrieved.

The storage and retrieval system 100 may be configured for installationin, for example, existing warehouse structures or adapted to newwarehouse structures. In the embodiments, the storage and retrievalsystem may include in-feed and out-feed transfer stations 170, 160,multilevel vertical conveyors 150A, 150B, a storage structure 130, and anumber of autonomous transport vehicles or robots 110 (referred toherein as “bots”). In the embodiments the storage and retrieval systemmay also include robot or bot transfer stations (as described in, forexample, U.S. patent application Ser. No. 12/757,220, entitled “STORAGEAND RETRIEVAL SYSTEM,” filed on Apr. 9, 2010, the disclosure of which isincorporated by reference herein in its entirety) that may provide anindirect interface between the bots 110 and the multilevel verticalconveyor 150A, 150B. The in-feed transfer stations 170 and out-feedtransfer stations 160 may operate together with their respectivemultilevel vertical conveyors 150A, 150B for bi-directionallytransferring case units to and from one or more levels of the storagestructure 130. It is noted that while the multilevel vertical conveyors150 are described herein as being dedicated inbound or in-feed conveyors150A and outbound or out-feed conveyors 150B, each of the conveyors150A, 150B may be used for both inbound and outbound transfer of caseunits/items from the storage and retrieval system. The multilevelvertical conveyors 150 may be any suitable lifting devices fortransporting case units between levels of the storage and retrievalsystem. It is noted that while multilevel vertical conveyors aredescribed herein in other aspects the conveyors may be any suitableconveyors or transfer/picking devices having any suitable transport pathorientation. Some non-limiting suitable examples of multilevel verticalconveyors can be found in, for example, U.S. Provisional PatentApplication No. 61/423,298, entitled “MULTILEVEL VERTICAL CONVEYORPLATFORM GUIDES” (-#1) and filed on Dec. 15, 2010, and U.S. patentapplication Ser. No. 12/757,354, entitled “LIFT INTERFACE FOR STORAGEAND RETRIEVAL SYSTEMS” and filed on Apr. 9, 2010 (the disclosures ofwhich are incorporated by reference herein in their entireties) and U.S.patent application Ser. No. 12/757,220, entitled “STORAGE AND RETRIEVALSYSTEM,” (previously incorporated by reference). For example, themultilevel vertical conveyors may have any suitable number of supportshelves for transporting the case units to a predetermined level of thestorage and retrieval system. In the embodiments transfer of case unitsbetween the bots 110 and the multilevel vertical conveyors may occur inany suitable manner through any suitable interface between the bots 110and the conveyors.

As may be realized, the storage and retrieval system 100 may includemultiple in-feed and out-feed multilevel vertical conveyors 150A, 150Bthat are accessible by, for example, bots 110 on each level of thestorage and retrieval system 100 so that one or more case unit(s) can betransferred from a multilevel vertical conveyor 150A, 150B to eachstorage space on a respective level and from each storage space to anyone of the multilevel vertical conveyors 150A, 150B on a respectivelevel. The bots 110 may be configured to transfer the case units betweenthe storage spaces and the multilevel vertical conveyors with one pick(e.g. substantially directly between the storage spaces and themultilevel vertical conveyors). By way of further example, thedesignated bot 110 picks the case unit(s) from a shelf of a multilevelvertical conveyor, transports the case unit(s) to a predeterminedstorage area of the storage structure 130 and places the case unit(s) inthe predetermined storage area (and vice versa).

The bots 110 may be configured to place case units, such as the abovedescribed retail merchandise, into picking stock in the one or morelevels of the storage structure 130 and then selectively retrieveordered items for shipping the ordered items to, for example, a store orother suitable location. In the embodiments, the bots 110 may interfacein any suitable manner with the multilevel vertical conveyors 150A, 150Bsuch as through, for example, extension of a transfer arm or effector110A (FIG. 3A) of the bot relative to a frame of the bot. Suitableexamples of bots are described in U.S. patent application Ser. No.12/757,312, entitled “AUTONOMOUS TRANSPORTS FOR STORAGE AND RETRIEVALSYSTEMS” and filed on Apr. 9, 2010, U.S. Provisional Patent Applicationentitled “BOT PAYLOAD ALIGNMENT AND SENSING” (-#1) (Ser. No. 61/423,220)and filed on Dec. 15, 2010 (PAR) with U.S. Ser. No. 13/327,040 filed onDec. 15, 2011), U.S. Provisional Patent Application entitled “AUTOMATEDBOT WITH TRANSFER ARM” (-#1) (Ser. No. 61/423,365) and filed on Dec. 15,2010 (PAR) with U.S. Ser. No. 13/326,952 filed on Dec. 15, 2011), andUnited States Provisional Patent Application entitled “AUTOMATED BOTTRANSFER ARM DRIVE SYSTEM” (-#1) (Ser. No. 61/423,388) and filed on Dec.15, 2010 (PAR) with U.S. Ser. No. 13/326,993 filed on Dec. 15, 2011),the disclosures of which are incorporated by reference herein in theirentireties.

The storage structure 130 may include multiple levels of storage rackmodules where each level includes an array of storage spaces (arrayed onthe multiple levels and in multiple rows on each level), picking aisles130A formed between the rows of storage spaces, and transfer decks 130B.In the embodiments, each level may also include respective bot transferstations for providing an indirect interface between the bots and themultilevel vertical conveyors. In this exemplary embodiment, the pickingaisles 130A and transfer decks 130B may be arranged for allowing thebots 110 to traverse respective levels of the storage structure 130 forplacing case units into picking stock and to retrieve the ordered caseunits. As may be realized, the storage and retrieval system may beconfigured to allow random accessibility to the storage spaces. Forexample, all storage spaces in the storage structure 130 may be treatedsubstantially equally when determining which storage spaces are to beused when picking and placing case units from/to the storage structure130 such that any storage space of sufficient size can be used to storeitems. The storage structure 130 of the embodiments may also be arrangedsuch that there is no vertical or horizontal array partitioning of thestorage structure. For example, each multilevel vertical conveyor 150A,150B is common to all storage spaces (e.g. the array of storage spaces)in the storage structure 130 such that any bot 110 can access eachstorage space and any multilevel vertical conveyor 150A, 150B canreceive case units from any storage space on any level so that themultiple levels in the array of storage spaces substantially act as asingle level (e.g. no vertical partitioning). The multilevel verticalconveyors 150A, 150B can also receive case units from any storage spaceon any level of the storage structure 130 (e.g. no horizontalpartitioning). In the embodiments the storage and retrieval system mayalso be configured so that each multilevel vertical conveyor serves apredetermined area of the array of storage spaces.

The storage structure 130 may also include charging stations 130C forreplenishing, for example, a battery pack of the bots 110. The chargingstations 130C may be located at, for example, transfer areas 295 (FIG.2) of the transfer deck 130B so that the bots 110 can substantiallysimultaneously transfer items, for example, to and from a multilevelvertical conveyor 150A, 150B while being charged. The bots 110 and othersuitable features of the storage and retrieval system 100 may becontrolled by, for example, one or more central system control computers(e.g. control server) 120 through, for example, any suitable network180. The network 180 may be a wired network, a wireless network or acombination of a wireless and wired network using any suitable typeand/or number of communication protocols. It is noted that, in oneexemplary embodiment, the system control server 120 may be configured tomanage and coordinate the overall operation of the storage and retrievalsystem 100 and interface with, for example, a warehouse managementsystem 125, which in turn manages the warehouse facility as a whole. Thecontrol server 120 may be substantially similar to that described in,for example, U.S. patent application Ser. No. 12/757,337, entitled“CONTROL SYSTEM FOR STORAGE AND RETRIEVAL SYSTEMS” and filed on Apr. 9,2010, the disclosure of which is incorporated by reference herein in itsentirety.

Referring also to FIG. 2, an exemplary configuration of the storage andretrieval system 100 is shown. Other suitable exemplary configurationsof storage and retrieval systems can be found in, for example, U.S.patent application Ser. No. 12/757,381, entitled “STORAGE AND RETRIEVALSYSTEM” and filed on Apr. 9, 2010, and United States Provisional PatentApplication entitled “Warehousing Scalable Storage Structure” (-#1)(Ser. No. 61/423,340) and filed on Dec. 15, 2010 (PAR) with U.S. Ser.No. 13/326,674 filed on Dec. 15, 2011), the disclosures of which areincorporated by reference herein in their entireties. It should beunderstood that in the embodiments the storage and retrieval system mayhave any suitable configuration. As can be seen in FIG. 2, the storageand retrieval system 200 is configured, for exemplary purposes only, asa single-ended picking structure in which only one side of the system200 has a transfer section or deck 130B. The single-ended pickingstructure may be used in, for example, a building or other structurehaving loading docks disposed only on one side of the building. In thisexample, the storage and retrieval system 200 includes transfer deck(s)130B and picking aisles 130A that allow bots 110 to traverse an entiretyof a level of the storage structure 130 on which that bot 110 is locatedfor transporting items between any suitable storage locations/pickingaisles 130A and any suitable multilevel vertical conveyors 150A, 150B.The multilevel vertical conveyors 150A, 150B provide transport of caseunits into the storage and retrieval system 200 through inputworkstations 210 and provide output of case units from the storage andretrieval system 200 through output workstations 220. The storage andretrieval system 200 includes a first and second storage section 230A,230B located side by side so that the picking aisles of each section aresubstantially parallel with each other and facing the same direction(e.g. towards transfer deck 130B). In the embodiments the storage andretrieval system may have any suitable number of storage sectionsarranged relative to each other in any suitable configuration.

Referring to FIGS. 3A-3C, as described above, the bots 110 areconfigured to traverse the transfer deck(s) 130B and picking aisles130A. The speed at which the bot 110 travels along the transfer deck(s)130B may be higher than the speed at which the bot travels in thepicking aisles. In the embodiments the bot 110 may travel at anysuitable speeds within the travel decks and picking aisles. On thetransfer decks 130B the bots 110 may be expected to travel at speeds upto about 10 m/s and higher speeds may be desired. The bot may travelalong the transfer deck 130B in an unconstrained or unrestricted manner(e.g. substantially without mechanical guidance such as tracks, rails,etc.) while the bot 110 may be guided by, mechanical guide constraintssuch as tracks or rails during travel within the picking aisles 130Asuch as, for example, described in U.S. patent application Ser. No.12/757,312, previously incorporated by reference. The bot may includeany suitable sensors, such as one or more line following sensors 380A,380B and one or more wheel encoders 381, 382, for providing feedback to,for example, bot controller 1220 for guiding the bot along one or moreof the transfer deck(s) 130B and picking aisles 130A. In the embodimentsthe bot controller 1220 may be located on board the bot 110 and/or belocated remotely from the bot 110 but in, for example, bi-directionalcommunication with the bot 110. In one example the control server 120may act at least in part as the remotely located bot controller.

The bot 110 may include at least two independently driven drive wheels1211, 1212 and at least one swivelable (not steered, i.e., not providedwith an independent steering input) wheel or caster 1262, 1261. Inanother aspect, the drive wheels 1211, 1212 may be driven by a commonmotor and a transmission that is capable of providing or generatingdifferential torque in any suitable manner to the commonly driven wheelsfor a desired yaw input. It is noted that the casters 1261, 1262 and thedrive wheel 1211, 1212 are disposed at substantially oppositelongitudinal (e.g. front to back) ends of the bot 110 where a wheel islocated substantially at each of the four corners of the bot. Thiscaster wheel/drive wheel configuration may provide improved high speedstability for the bot and ease of control. Each drive wheel 1211, 1212may have its own respective motor 383, 384 that is controlled by the botcontroller 1220 in the manner described herein. As will be described ingreater detail below, the casters 1262, 1261 may be selectively lockedto allow stable travel of the bot 110 during, for example, substantiallyhigh speed bot travel along the transfer deck 130B. It is noted thatduring low speed travel the casters 1262, 1261 may be unlocked so thatthe bot 110 can enter, for example, picking aisles and/or multilevelvertical conveyor interface stations with either a front or a back ofthe bot 110 leading a direction of bot travel as described in, forexample, U.S. Provisional Patent Application entitled “AUTONOMOUSTRANSPORT VEHICLE” (-#1) (Ser. No. 61/423,409) and filed on Dec. 15,2010 (PAR) with U.S. Ser. No. 13/326,423 filed on Dec. 15, 2011), thedisclosures of which are incorporated by reference herein in theirentireties. Steering of the bot 110 along the transfer deck may beeffected by applying a differential torque to the drive wheels 1211,1212 through the respective independently controller motors 383, 384.The differential torque T may result in each of the drive wheelsrotating at different speeds (e.g. rotations). The different rotationalspeeds of each wheel may cause the bot 110 to yaw or turn.

As an example of bot travel along the transfer deck and referring toFIGS. 3C and 5, during straight line travel of the bot along, forexample, guide line 395 (e.g. in 1 degree of freedom) both drive wheels1211, 1212 rotate at substantially the same speed/angular velocity. Ifthe travel direction of the bot has to be corrected for any suitablereason, one of the drive wheels 1211, 1212 may be slowed down to causeyawing of the bot. For example, if the bot 110 is to turn or yaw in thedirection of arrow 396 the bot controller 1220 may cause drive wheel1211 to rotate slower than drive wheel 1212 for turning the bot 110 inthe direction of arrow 396. Likewise, if the bot 110 is to turn or yawin the direction of arrow 397 the bot controller 1220 may cause drivewheel 1212 to rotate slower than drive wheel 1211 for turning the bot110 in the direction of arrow 397. It is noted that the bot 110 iscapable of bidirectional travel along guide line 395.

In the embodiments, as described above, the bot 110 may include one ormore line following sensors 380A, 380B configured to detect one or moreguidance lines 391-395 (which are inclusive of guide lines 391A whichmay be disposed on the transfer deck 130B at predetermined intervals ina direction transverse to the bot travel along the transfer deck may beprovided as shown in FIG. 5) such as line 395 disposed on a surface of,for example, the transfer deck 130B for providing steering feedback tothe bot controller 1220. It is noted that the one or more line followingsensors 380A, 380B may be located at the front and rear of the bot 110or the line following sensors may be located in any suitable location onthe bot. The bot controller 1220 may be configured to receive signalsgenerated by the one or more line following sensors 380A, 380B and orwheel encoders 381, 382 from which the controller 1220 determinessuitable torque commands for driving the respective motors 383, 384 ofdrive wheels 1211, 1212.

The casters 1261, 1262 may be un-steered as noted before, but may have adirectional or swivel lock configured to aid in steering and control ofthe bot 110. It is noted that during substantially straight line travelof the bot on the transfer deck 130B the casters 1261, 1262 may belocked (e.g. the plane of rotation of the caster wheel 400 issubstantially aligned with a 1 degree of freedom axis 110X of the botwhere the 1 degree of freedom axis 110X may coincide with the bot'sstraight line direction of travel) unless the degree at which the bot110 is to turn (e.g. to account for corrections to the direction oftravel) exceeds a predetermined amount (e.g. a predetermined turn anglefor correcting tracking of the substantially straight line travel of thebot) or if the bot travel speed is below a predetermined amount. Thecasters may also be unlocked to provide the bot with steering that ismore responsive than when the casters are locked so that quickercorrections to the bot's direction of travel can be made. It is notedthat, as shown in FIG. 5, the positioning of the casters 1261, 1262 atan end of the bot 100 that is opposite the drive wheels 1211, 1212operates to amplify the slip angle or amount of lateral movement at,e.g. a front of the bot where the casters are located. The slip angle oramount of lateral movement may be generated from the differentialrotation at the drive wheels 1211, 1212. The slip angles will generallybe small, and thus can be generated by correspondingly smallerdifferential rotation at the drive wheels which minimizes slipping ofthe drive wheels (which is undesirable). The slipping of the casterwheels may occur when the swivel lock of the casters is locked and adifferential torque is applied to the drive wheels such that the casterwheels are “slid” in a direction substantially transverse to a plane ofrotation of the caster wheel as it travels along, e.g., the transferdeck 130B. During the slipping of the caster wheel it is noted that thecaster wheel may slow its rotation or substantially stop rotating.

Still referring to FIGS. 3A-3C and 5 as a non-limiting example only, thebot may travel on the transfer deck 130B along line 395 where the bot isto turn down picking aisle 130A1 in a manner substantially similar tothat described in U.S. patent application Ser. No. 12/757,312(previously incorporated by reference herein). The casters 1261, 1262may be locked to allow for stable high speed bot travel until the botmakes or is about to make the turn onto the picking aisle 130A1. Forexample, as the bot slows below a predetermined travel speed, thecasters 1261, 1262 may unlock allowing the caster wheels to swivel (e.g.giving the bot 2-degrees of freedom of movement). The bot controller1220 may also determine that the bot is to make a turn (such as thesubstantially 90-degree turn into picking aisle 130A1) where the angleof the turn exceeds a predetermined turn angle. The casters 1261, 1262may unlock upon the determination that the turn angle exceeds thepredetermined turn angle for correcting tracking of the substantiallystraight line travel of the bot. The bot controller 1220 may alsoaccount for turn angle and bot speed when determining when to unlock thecasters 1261, 1262. The controller 1220 may also be configured to causethe unlocking of the casters 1262, 1261 at substantially the same timethat a differential torque is applied to the drive wheels 1211, 1212.

Referring now to FIGS. 4A-4E the swiveling caster wheels 1261, 1262having the selectively lockable swivel lock will be described. It isnoted that while the casters are described with respect to caster 1262,caster 1261 is substantially similar. In accordance with theembodiments, the caster 1262 includes a frame 412, a wheel yoke 410, awheel 400, a first locking member 440, a second locking member 450, anactuator 420 and a spring 430. It is noted that the caster may have anysuitable components arranged in any suitable manner. In this example,the wheel 400 is rotatably mounted to the yoke 410 in any suitablemanner. The second locking member 450 may be fixedly mounted to the yoke450 so that the second locking member 450 and yoke 410 form an integralunit. In the embodiments the second locking member may be integrallyformed with the yoke 410 in a unitary construction. The yoke 410 (andthe second locking member 450 mounted thereto) may be pivotally mountedto the frame 412 so that the yoke assembly (e.g. including the secondlocking member 450, the yoke 410 and the wheel 400) can be freelyrotated 360-degrees in the direction of arrow 499 (see also FIG. 3B). Itis noted that the axis of rotation of the yoke assembly is substantiallyperpendicular to a surface on which the bot 110 travels, such as, forexample, the surface of the transfer deck 130B. The first locking member440 may be pivotally mounted to the frame 412 by, for example, anysuitable pivot 441 having a pivot axis that is substantially parallelwith a swivel axis of the yoke 450 (and wheel 400). The pivot 441 may befor example, a shoulder bolt or any other suitable axle and/or retainingdevice. A spring 430 or any other suitable resilient member may bemounted between the frame 430 and a portion of the first locking member440 so as to bias the first locking member 440 about the pivot 441 aswill be described in greater detail below. The actuator 420 may also bemounted to the frame 412 for engaging a portion of the first lockingmember 440 in an opposing relation to the spring 430. The actuator 420may be any suitable actuator, such as a solenoid, suitably connected to,for example, the bot controller 1220 where the controller is configuredto cause actuation of the actuator 420. In one aspect the actuator 420may be horizontally oriented (e.g. arranged to extend and retracthorizontally) but in other aspects the actuator may have any suitableorientation. The swivel lock of the casters 1262, 1261 may be configuredfor rapid lock and release through, for example, a pulse actuation ofthe actuator 420 (e.g. electrical current is sent to the actuator for apredetermined amount of time so that the actuator is activated only fora limited time so that a piston 420P of the actuator is retracted forreleasing the swivel lock of the caster and extended for locking theswivel lock of the caster in succession). In one example, the pulseactuation of the actuator 420 may activate the actuator forapproximately one or two seconds for unlocking the swivel lock of thecasters. In other examples the pulse actuation of the actuator mayactivate the actuator for less than about one second. In still otherexamples, the pulse actuation of the actuator may activate the actuatorfor more than about two seconds or any other suitable amount of time.The actuator may also be configured so that the caster is released whenthe piston 420P is extended and locked when the piston 420P isretracted. As may be realized, in one example, any suitable sensors maybe provided and be in communication with the controller 1220 for sensingwhen each of the swivel locks for the casters is locked and/or unlocked.In other examples, sensors may not be provided for sensing when thecasters are locked and/or unlocked.

In this exemplary embodiment the first locking member or lock bar/link440 may have a substantially dog-leg or hooked shape. In alternateembodiments the first locking member 440 may have any suitable shape.The first locking member 440 may have a pivot hole 440H configured toaccept the pivot 441 for allowing the first locking member to pivotabout the pivot pin 441. A first portion 440B of the first lockingmember 440 may extend in a first direction from the pivot hole 440Hwhile a second portion 440C of the first locking member 440 extends in asecond direction from the pivot hole 440H. The first direction andsecond direction may be angled relative to one another by any suitableangle (e.g. from 0 to 360 degrees). In this example, the first portion440B includes a protrusion or other locking feature 440L configured toengage a reciprocally shaped engagement feature 450S1, 450S2 of thesecond locking member 450. The second portion 440C may include anattachment feature 440S for attaching the spring 430 to the firstlocking member 440. The second portion 440C may also include an actuatorengagement surface 440A. In this example, the ratio between the lengthsof the first and second portions 440B, 440C of the first locking membermay be such that forces applied to the second portion 440C cause theprecise movement of the first portion 440B for releasing locking feature440L from the second locking member 450. For example, the lever actionof the first locking member 440 converts the stroke of the actuator 420to a short engagement stroke of the protrusion 440L into and out of theone or more engagement features 450S1, 450S2 that may result insubstantial on/off control of the swivel lock to reliably engage anddisengage the swivel lock while the bot is travelling at speed (e.g.about 10 m/s or more) and/or while the bot is travelling at any suitablespeed.

In the embodiments the second locking member 450 is in the form of adisc but the second locking member may have any suitable configuration.The second locking member may include one or more engagement features orslots 450S1, 450S2 or other retaining feature configured to accept andreciprocally engage the protrusion 440L of the first locking member 440or the second locking member may include a protrusion for engaging areciprocally engagement feature or recess in the first locking member.In the embodiments, the second locking member may include two slotsarranged so that the caster wheel 400 can be locked at about 0-degreesand about 180-degrees where the about 0 and 180-degree positions arearranged so that when locked the rotational plane of the wheel 400 issubstantially aligned with a 1-degree of freedom axis 110X of the bot(which may coincide with the direction of straight line travel of thebot 110). In the embodiments the second locking member may have anysuitable number of locking features arranged in any suitable manner forlocking the wheel at any angle(s).

In operation, to lock swivel lock of the caster 1262 the actuator may beretracted (e.g. a piston 420P or other suitable engagement feature ofthe actuator may be retracted) so that it is not in substantial contactwith the actuator engagement surface 440A of the first locking member440. The spring 430 may be configured to pull or otherwise bias thefirst locking member to rotate about pivot 441 in the direction of arrow495 so that the locking feature 440L is substantially forced against aside surface 450S of the second locking member 450. As the yoke assemblyrotates in the direction of arrow 499 and the biased locking feature440L rides along the side surface 450S the force exerted by the spring430 causes the locking feature 440L to be inserted into one of the slots450S1, 450S2 for substantially preventing further rotation of the yokeassembly such that the yoke assembly of the caster is in a lockedconfiguration (e.g. is locked from rotation). As noted above, the slots450S1, 450S2 may be positioned so that when the locking feature 440L isinserted into one of the slots 450S1, 450S2 the rotational plane of thewheel 499 is substantially aligned with the 1 degree of freedom axis110X of the bot. As such, one of the slots 450S1, 450S2 will be alignedwith the locking feature 440L by virtue of the bot travelling along asubstantially straight line path to facilitate the locking of the caster1262.

To unlock the swivel lock of the caster, the actuator 420 is actuated(e.g. the piston 420P or other engagement feature is extended in thedirection of arrow 491) to engage the actuator engagement surface 440Aof the first locking member 440. As described above, the actuation ofthe actuator 420 may be a pulse actuation (e.g. electrical current issent to the actuator for a predetermined amount of time so that theactuator is activated only for a limited time so that a piston 420P ofthe actuator is retracted for releasing the swivel lock of the casterand extended for locking the swivel lock of the caster in succession).The force exerted by the actuator 420 on the first locking member 440opposingly overcomes the force of the spring 430 causing the firstlocking member 440 to rotate about pivot 441 in the direction of arrow496 such that the locking feature 440L disengages the slot 450S1, 450S2for unlocking the swivel lock of the caster 1262. As a differentialtorque T is applied to the drive wheels the caster wheels 1262, 1261want to rotate according to the way the bot 110 is turning. Thedisengagement or release of the locking member 440L from the slot 450S1,450S2 allows the wheel 400 (e.g. through a rotation of the components ofthe yoke assembly) to freely rotate or swivel in the direction of arrow499 by virtue of the differential torque applied to the drive wheels1211, 1212. It is noted that the actuator is activated for a time periodthat is long enough for the slot 450S1, 450S2 to become misaligned withthe locking feature 440L after which time the spring 430 causes thelocking feature 440L to ride along the side 450S as described above toallow for unlocking and locking of the caster 1262, 1261 as describedabove.

As can be seen in e.g. FIGS. 4A-4E, the configuration of the firstlocking member 440 is such that locking engagement between the first andsecond locking members 440, 450 occurs substantially laterally relativeto the longitudinal axis or 1-degree of freedom axis of the bot 110 forincreased rigidity (e.g. creating a greater moment arm for resistingrotation of the yoke assembly). However, the first locking member (andsecond locking member) may have any suitable configuration and spatialrelationship with each other and the 1-degree of freedom axis of the botfor rigidly preventing rotation of the caster 1262, 1261. In theembodiments, a caster drive motor may be coupled to, for example, theyoke assembly, for providing steerable rotational movement of the caster1262, 1261. It is noted that the coupling between the caster drive motorand the yoke assembly may be any suitable coupling includingsubstantially rigid links, belts/pulleys, gear trains and any othersuitable drive couplings.

Referring again to FIG. 3C and as described above, the bot 110 mayinclude one or more wheel encoders 381, 382 configured to senserotational movement of each of the drive wheels 1211, 1212. The wheelencoders 281, 282 may be any suitable encoders such as, for example,incremental encoders. In the embodiments the encoders may also beabsolute encoders. In this example, the encoders 381, 382 provide datato, for example, the bot controller 1220 for determining a location ofthe bot 110 within the storage and retrieval system 100. An example ofdetermining the location of the bot 110 within the storage and retrievalsystem 100 using encoders can be found in U.S. Provisional PatentApplication entitled “BOT POSITION SENSING” (-#1) (Ser. No. 61/423,206)and filed on Dec. 15, 2010 (PAR) with U.S. Ser. No. 13/327,035 filed onDec. 15, 2011), the disclosures of which are incorporated by referenceherein in their entireties. The encoders 381, 382 on each of the drivewheels may also provide information for determining a state (e.g.acceleration, speed, direction, etc.) of the bot 110 as will bedescribed below. However, the drive wheels 1211, 1212 may be subject towheel slipping that adversely affects the confidence of the datareceived from the encoders 381, 382. Wheel slipping may be caused by,for example, a loss of traction. This loss of traction may be caused by,for example, a reduction in friction between each of the drive wheels1211, 1212 and the drive surface of, for example, the transfer deck 130Bor picking aisle 130A or one of the drive wheels 1211, 1212 lifting offof the drive surface of the transfer deck 130B or picking aisle 130A.Where the bot drive wheels 1211, 1212 lose traction the wheel positionmeasured by the respective encoders 381, 382 will no longer reflect theactual bot 110 position. For example, if the bot 110 is acceleratingthen the wheel will tend to rotate faster than the bot is travelling.Conversely, if the bot is decelerating then the slipping wheel will tendto rotate slower than the bot is travelling.

In accordance with the embodiments, the bot controller 1220, or anyother suitable controller of the storage and retrieval system (e.g.control server 120) may be configured to account for wheel slip by, forexample, using the data from the encoder 381, 382 from the drive wheel1211, 1212 that is not slipping. In one example, the controller 1220 maybe configured to determine which drive wheel 1211, 1212 is slippingbased on the torque being applied to the drive wheels 1211, 1212 bytheir respective drive motors 383, 384. As a non-limiting example, if apositive torque is being applied then a slipping wheel will acceleratein a positive manner so the encoder from the wheel with a lower velocityand/or rotational speed will be used to estimate the speed and positionof the bot 110 within the storage and retrieval system 100. If anegative torque is being applied to the drive wheels 1211, 1212 then aslipping wheel will accelerate in a negative manner (e.g. decelerate) sothe encoder from the drive wheel 1211, 1212 with a higher rotationalvelocity and/or rotation speed will be used to estimate the speed andposition of the bot 110 within the storage and retrieval system 100. Inthe embodiments, one or more encoders may be placed on idler wheels(e.g. wheels that are not driven) such as the casters 1261, 1262 suchthat the controller can estimate the position and speed of the bot 110based on the rotation of the non-driven wheels.

In the embodiments, the controller 1220 may be configured withpredetermined drive wheel 1211, 1212 velocities or rotational speeds forany predetermined time of bot operation. The controller 1220 whendetermining the position and speed of the bot 110 when, for example, onewheel is slipping may compare the actual velocities and/or rotationalspeeds of the drive wheels 1211, 1212 with the expected or predeterminedvelocities and/or rotational speeds for each drive wheel 1211, 1212. Inone example, the controller 1220 may be configured to perform inertiamodeling to determine how much velocity/rotation speed change to expectdue to, for example, acceleration of the bot 110 (and its drive wheels).If the velocities/rotational speeds of one or more of the drive wheels1211, 1212 does not substantially match the expected or predeterminedvelocities/rotational speeds the encoder data from the one or more ofthe drive wheels 1211, 1212 whose data does not substantially match maybe ignored and replaced with the expected or predetermined data whendetermining the bot's 100 position and speed.

It is noted that the determination of the bot's speed and position maybe performed with, for example, models that both utilize and do notutilize suitable filters. In the embodiments the controller 1220 may beconfigured to filter the spurious data from the drive wheel encoders381, 382 when determining bot 110 location/speed and state estimations.As an example, the controller 1220 may include, for example, a Kalman(or other suitable) filter to substantially eliminate the effects ofwheel slip error in bot state estimation and location calculations. Inone aspect the controller 1220 may include an extended Kalman filter1220K that may be employed using substantially real time encoder updates(for example, at 2 kHz, every 0.5 milliseconds, every 50 milliseconds,or any other suitable frequency or time increments), along with anysuitable time data regarding each sensor transition event (e.g. such aswhen a sensor detects a suitable guide line, see FIG. 5 on the transferdeck 130B). Referring to FIG. 6 a bot position determination methodemploying an extended Kalman filter is depicted. In general, calculatinga bot 110 position may be performed using an extended Kalman filter byapplying data received from any suitable encoder (FIG. 6, Block 16000),such as one or more of encoders 381, 382, to determine the bot 110position and/or predict sensor 380A, 380B transitions. However, as avariation to the general method depicted in FIG. 6, the bot positionfinding Kalman model may be updated periodically. More specifically,sensor data may be received at each sensor 380A, 380B transition over asuitable guide line, such as guide lines 391-394 (as may be realized,additional guide lines 391A that are disposed on the transfer deck 130Bat predetermined intervals in a direction transverse to the bot travelalong the transfer deck may be provided as shown in FIG. 5), thatincludes a time of the transition and as appropriate, an identity and/orlocation of the guide line (FIG. 6, Block 16001). Based upon the datafrom sensors 380A, 380B, an error may be calculated between an expectedtransition time for the location and the measured transition time (FIG.6, Block 16002). This error may then be employed to update the extendedKalman filter for more accurate subsequent estimations of botpositioning as determined by the wheel encoders 381, 382 (FIG. 6, Block16003). In general, one or more of the wheel encoder and line sensordata is employed to provide bot positioning data for control of the bot110, while actual detected guide line transitions may be employed toupdate the pot positioning model, for example, the equations of anextended Kalman filter.

By way of example, for bot positioned at a particular position (Xe, Ye)on, for example the transfer deck 130B, and travelling at an estimatedvelocity and acceleration V, a, the model might predict a guide linebeing sensed or transitioned by one of the line sensors 380A, 380B attime t_(e), and the system may identify the actual transition of theguide line at time t_(s). The encoder 381, 382 time t_(s) (or optionallyat the time stamp) may generate an error expressed as:

$\delta \equiv {t_{s} - {t_{e}\mspace{14mu}{or}\mspace{14mu}\underset{\_}{\delta}}} \equiv {\begin{bmatrix}t \\x \\y\end{bmatrix}_{s} - \begin{bmatrix}t \\x \\y\end{bmatrix}_{e}}$

Then, extended Kalman filter equations may be used as described forexample, in Applied Optimal Estimation by Arthur Gelb (MIT Press 1794).An adaptation of the formulation described in Gelb may be briefly statedas a system model:{dot over (x)}(t)=f(x(t),t)+w(t);w(t)≈N(0,Q(t))and a measurement model:z _(k) =h _(k)(x(t _(k)))+v _(k) ; l=1, 2, . . . v _(k) ≈N(0,R _(k))with state estimate propagation:{circumflex over (x)}(t)=f({circumflex over (x)}(t),t)and error covariance propagation:{dot over (P)}(t)=F({circumflex over (x)}(T),T)P(t)F ^(T)({circumflexover (x)}(t),t)+Q(t)

As a significant advantage, this generalized technique permits use ofindividual sensor events incrementally, rather than requiring somenumber of sensor event to identify the location of the bot 110. Itshould be understood that, while a particular order of steps is impliedin FIG. 6, that the depicted operations are repetitively performedduring operation of the bot 110, and that no particular order or timingof steps should be inferred. Nonetheless, it will be generally true insome implementations that encoder data from wheel encoders 381, 382 maybe provided substantially continuously in real time, while line sensor380A, 380B transitions of guide lines 391-394 (and 391A) may occurintermittently as the bot traverses, for example the transfer deck 130B.It should also be understood that, while an extended Kalman filter isone useful technique for converting encoder data into bot positioninformation, other filters or linear modeling techniques may similarlybe applied.

The data from the encoders 381, 382 may be further weighted based onsignals from the one or more line following sensors 380A, 380B thatprovide signals to the controller 1220 corresponding to deviation of thebot from a guide line GL (FIG. 5) on, for example, the transfer deck130B. For example, when one of the drive wheels 1211, 1212 slips adifferential torque results between the drive wheels 1211, 1212 whichcauses the bot 110 to turn and deviate from the guide line GL.

The bot controller 1220 may also be configured to determine a positionof the bot using, for example, the wheel encoders 381, 382 incombination with other position tracking features of the storage andretrieval system. In the embodiments, when in the picking aisles 130Athe wheel encoders 381, 382 may be used in combination with slatcounting (e.g. tracking the position of the bot relative to slats on thestorage shelves with one or more slat detection sensors 387) asdescribed in U.S. Provisional Patent Application No. 61/423,206 entitled“BOT POSITION SENSING” (-#1), previously incorporated by referenceherein. In the embodiments, when travelling on the transfer deck 130Bthe controller 1220 may be configured to use the wheel encoders 381, 382in combination with a tracking of the guide lines 391-395 on the floor(e.g. driving surface) of the transfer deck 130B. Referring to FIGS. 3Cand 5 when travelling on the transfer deck 130B the one or more linefollowing sensors 380A, 380B of the bot detect guide lines 391-395 (FIG.7, Block 17000). The controller 1220 receives signals from the one ormore line following sensors 380A, 380B (FIG. 7, Block 17001) and drivesthe individual drive motors 383, 384 accordingly (e.g. by adjusting thetorque applied to each respective wheel for steering the bot asdescribed above) for keeping the bot travelling along a desired one ofthe guide lines 391-395 (FIG. 7, Block 17002). As can be seen in FIG. 5,each guide line GL running around the transfer deck 130B is crossed by,for example, transverse guide lines, such as guide line 392 located atturns on the transfer deck as well as guide lines 391, 393, 394 locatedat the picking aisle 130A locations. The crossing locations R, P of eachof these guide lines 391-395 may be at known predetermined locationswhich are stored in any suitable memory accessible by the bot 110 suchas for example, a memory of the bot 110 or the control server 120. Wherethe crossing locations R, P are stored remotely from the bot 110, suchas in a memory of the control server, the bot 110 may be configured toaccess the crossing location information in any suitable manner suchthat the information is downloaded to the bot 110 or remotely read bythe bot 110.

In one exemplary operation of bot travel, it is noted that verificationor position qualification of the bot 110 on, for example, the transferdeck 130B may be determined from the crossing locations/position datumlines R, P on the transfer deck 130B (FIG. 7, Block 17003) in a mannersubstantially similar to that described in U.S. patent application Ser.No. 12/757,312 (previously incorporated by reference herein). Forexample, as the bot 110 travels along, for example, guide line 395 thebot passes the crossing location P and may verify its location using thepredetermined location of the crossing location P. At this point thedata from the wheel encoders may be reset (FIG. 7, Block 17004) so thatthe encoders incrementally track, for example, a distance traveled bythe bot 110 starting from crossing location P (which was previouslyverified) so that, for example, the controller 1220 can estimate the botposition relative to a last known verified position of the bot (FIG. 7,L. 17005). It is noted that resetting the wheel encoder data maysubstantially eliminate any tolerance and/or error stack ups generatedby the wheel encoders. As the bot 110 continues to travel along theguide line 395 the bot 110 detects a second crossing location R. Atsubstantially the time the second crossing location R is detected by thebot 110 the controller 1220 uses an estimated location of the bot 110 asdetermined from the wheel encoders 381, 382 and the last verifiedlocation of the bot (which in this example is at crossing location P)and compares the estimated location of the bot with the predeterminedlocation of the crossing location R (FIG. 7, Block 17006). If theestimated location of the bot substantially matches the predeterminedlocation of the crossing location R then the controller verifies orotherwise qualifies the position of the bot 110 and updates the bots 110location accordingly (FIG. 7, Block 17007). The controller 1220 may alsobe configured to verify or otherwise qualify the bot's location in anysuitable manner such as, for example, through the use of an extendedKalman filter as described above. As may be realized during thedetermination of the bot's position/location using the wheel encoders381, 382 and line following the controller 1220 may be configured toaccount for wheel slip in the manner described above. If the estimatedposition does not match the predetermined location of the crossinglocation R the signal generated by the one or more line followingsensors 380A, 380B corresponding to guide line 394 (at location R) maybe ignored such that the location of the bot is estimated using thewheel encoders 381, 382 (FIG. 7, Block 17008) until a next crossinglocation can be verified or otherwise qualified with the bot's estimatedlocation (FIG. 7, Blocks 17006, 17007). In the embodiments, if theestimated location of the bot 110 and the predetermined crossinglocation do not match the bot 110 may also be configured to verify itsposition in any suitable manner such as, for example, returning to alast known location and resetting the encoder information.

Referring to FIGS. 3C and 5, the bot controller 1220 (or other suitablecontroller configured to control the bot, such as a remote controller asdescribed above) may be configured with a state estimator module 1220Efor estimating, for example, the kinematic state of the bot (e.g.position X, Y; position rates or speed {dot over (x)}, {dot over (y)},and/or yaw angle α all with respect to time t) to determine commandlogic for controlling the bot rather than controlling the bot directlyfrom sensor input. For example, using the state estimator module 1220Ethe bot 110 can determine, based on one or more sensor inputs, how fastit is travelling, what direction it is travelling, etc. and thendetermine what bot parameters need to be changed in order to arrive at anew desired speed, direction, etc. rather than, using bot speed as anexample, reduce the torque on the drive wheels and use the wheelencoders as a gauge for stopping the reduction in motor torque when theencoders send signals corresponding to the desired new speed.

In one example, the command logic may allow, for example, the controller1220 to know the speed, acceleration, and direction of the bot andcalculate corrective control commands to, for example, the drive motors383, 384 for maintaining a predetermined directional course and speed.For convention purposes, the Y (e.g. longitudinal) position of the botis in a direction substantially parallel with a predetermined datum lineor line of travel (in this example e.g. line 395) and may be anestimation of bot position between, for example, line crossing locationsR, P or any other suitable lateral datum lines. The X (lateral) positionof the bot is in a direction substantially transverse to thepredetermined datum line 391-395 and may be an estimation of the amountof offset between, for example, the 1 degree of freedom axis 110X of thebot and the predetermined datum line 391-395. The yaw angle α (e.g. thedivergence/convergence angle with the predetermined datum line) may bean estimation of the angle between the 1 degree of freedom axis 110X ofthe bot and the predetermined datum line 391-395. The state estimatormodule 1220E of the controller 1220 may also be configured to determineor otherwise estimate dynamic states and commands such as, for example,forces Fx, Fy exerted on the bot, the differential torque T applied bythe drive motors 383, 384, a position rate or speed of the bot (e.g.linear or angular/yaw speeds) and/or changes in the position rate (e.g.acceleration) of the bot 110.

In addition to the wheel encoders 381, 382 and line following sensors380A, 380B described above, the bot 110 may or may not also include anysuitable inertial sensor 389, such as a 1 or 2 dimensionalaccelerometer. The controller may be configured to use signals from theinertial sensor 389 in combination with, for example, wheel odometryinformation from the wheel encoders 381, 382 and the line followingsensors 380A, 380B for estimating the state of the bot 110.

Input may be provided to the controller 1220 for use with the stateestimator module 1220E from, for example, one or more of the wheelencoders 381, 382, the line following sensors 380A, 380B and theinertial sensor 389 (FIG. 8, Block 18000). Input may also be provided tothe controller for use with the state estimator from slat sensors (e.g.sensors that sense the storage shelf slats). An example, of storage slatsensors can be found in U.S. Provisional Patent Application No.61/423,206, entitled “BOT POSITION SENSING” (-#1), previouslyincorporated by reference herein.

In the embodiments the bot may have, for example, a steady state ofoperation (e.g. no acceleration/deceleration) and a dynamic state ofoperation (e.g. during acceleration/deceleration). During steady stateoperation with the differential motor torque T substantially equal tozero the state estimator may obtain data for longitudinal position Y andlongitudinal speed {dot over (y)} from, for example, wheel odometry asdescribed above (FIG. 8, Block 18001). It is noted that the longitudinalspeed {dot over (y)} may be obtained from the wheel encoders using, forexample, a Kalman or other suitable filter accounting for wheel slip asdescribed above. Lateral position X and lateral speed {dot over (x)} maybe obtained from, for example, the line following sensors 380A, 380Bwhen the line following sensors 380A, 380B at, for example, the frontand rear of the bot 110 cross the lines 393, 394, 391. The lateralposition X of the bot and the yaw angle α can be calculated from thefront and rear positions of the bot 110 as determined by the sensors380A, 380B when the sensors cross the lines 393, 394, 391 (FIG. 8, Block18002). In one example, between line 393, 394, 391 crossings thedifferential movement of the wheels (as determined from e.g. wheelencoders or other suitable sensors) indicate rotation or yaw of the bot.In another example, between line 393, 394, 391 crossings the rotation oryaw angle α of the bot 110 may be determined from a dynamic model in,for example, an extended Kalman filter. The lateral speed {dot over (x)}can be determined by the state estimator, for example, as follows:{dot over (x)}={dot over (y)} tan α

where {dot over (y)} may be verified using, for example, crossinglocations R, P or any other suitable transverse datum lines similar toguide lines 393, 394, 391.

Referring also to FIG. 4A-4E, in one exemplary embodiment the controller1220 may command actuation of the actuators 420 for unlocking thecasters 1262 based on the state of the bot 110 so that quick steeringresponse can be obtained for correcting the yaw angle α of the bot. Theyaw angle α of the bot may also be corrected with the casters locked,which may provide a slower steering response with more bot stability.The controller 1220 may know (via the state estimator module 1220E) anestimate of the differential torque T to apply to the drive wheels 1211,1212 so that a maximum differential torque T can be applied to the drivewheels 1211, 1212 for correcting the yaw angle α of the bot 110. It isnoted that the estimate for the transverse speed {dot over (x)} (or anyother suitable kinematics of the bot) can be updated (FIG. 8, Block18003) at any suitable time such as when, for example, there is no linesense signal from speed {dot over (y)} and yaw angle α. The yaw angle αand the rate of change of the yaw angle {dot over (α)} can be estimatedusing, for example, the inertial sensor 389.

Once the differential torque T is applied based on the estimated valueof the yaw angle α, the controller 1220 waits to receive a guide linesense signal from one or more of the line following sensors 380A, 380B.When the line sense signal is received, the controller 1220 may commanda reduction in differential torque T and continue to update thekinematic information of the bot 110 until the yaw angle α is at apredetermined value such that the bot is substantially travelling alongthe desired guide line 391-395. It is noted that the differential torqueT may be reduced proportionately to the approach rate (e.g. {dot over(x)}, {dot over (α)}) to, for example, the center of the guide line391-395. When the differential torque T is reduced to substantially zerothe bot is travelling in a substantially straight line enabling thecasters to lock into their locked configuration as described above (e.g.the locking feature 440L may ride along the side surface 450S of thesecond locking member 450 until it is substantially aligned with andengages one of the slots 450S1, 450S2. It is noted that when thedifferential torque T is applied, the transverse position X and speed{dot over (x)} may be determined by the controller 1220 (via the stateestimator module 1220E) from, for example, a mean of the wheel encodersignals where the differential torque T is known and the wheel encodersignals (from each drive wheel 1211, 1212) are related to one another(or otherwise weighted) based on the differential torque T such that,for example, a difference of inner to outer wheel encoder signals(depending on which way the bot is turning where the inner encoder is onthe inside of the turn) is applied to the encoder signal based on themagnitude of the differential torque T.

In the dynamic state of bot operation, e.g. where the bot 110 isundergoing positive acceleration or negative acceleration (i.e.deceleration) and the differential torque T is substantially zero orgreater than zero the kinematic state of the bot may be determined in amanner substantially similar to that described above with respect to thesteady state of bot operation. It is noted that where travel of the bot110 is guided by a contact linear guide system (e.g. tracks or rails) asin, for example, the picking aisles 130A (see for example, U.S. patentapplication Ser. No. 12/757,312, entitled “AUTONOMOUS TRANSPORTS FORSTORAGE AND RETRIEVAL SYSTEMS,” previously incorporated herein) there isno data sent to the controller 1220 by, for example, the line followingsensors 380A, 380B. As such, the state estimation of the bot 110 withinthe contact linearly guided travel areas is only in the longitudinaldirection. The position of the bot 110 within the picking aisles may bedetermined by the state estimator (without direct wheel encoderreadings) in combination with, for example, the storage shelf slatlocation validation as described in U.S. Provisional Patent ApplicationNo. 61/423,206 entitled “BOT POSITION SENSING” (-#1), previouslyincorporated by reference herein.

In a first aspect of the embodiments an autonomous transport vehicle fortransporting items in a storage and retrieval system is provided. Theautonomous transport vehicle includes at least two drive wheels and acontroller, where each drive wheel is independently driven and a drivewheel encoder is disposed adjacent each drive wheel. The controller, incommunication with the encoders, is configured to determine a kinematicstate of the autonomous transport vehicle within the storage andretrieval system based on incremental data from the drive wheel encodersonly and independent of drive wheel slippage.

In accordance with a first aspect of the first aspect of theembodiments, the controller is configured to determine command logic foroperating the autonomous transport vehicle based on the kinematic state.

In accordance with the first aspect of the first aspect of theembodiments, the autonomous transport vehicle includes one or more of awheel encoder for each drive wheel, an inertial sensor, at least onestorage slat sensor and at least one line following sensor, wherein thecontroller is configured to receive data from the one or more of thewheel encoder for each drive wheel, the inertial sensor, the at leastone storage slat sensor and the at least one line following sensor fordetermining the kinematic state.

In accordance with a second aspect of the first aspect of theembodiments, the controller is further configured to determine aposition of the autonomous transport vehicle within the storage andretrieval system independent of drive wheel slippage.

In accordance with the second aspect of the first aspect of theembodiments, the controller is configured to determine the position ofthe autonomous transport vehicle based on a drive wheel having a lowestvelocity of the at least two drive wheels when a positive torque isapplied by the at least two drive wheels.

In accordance with the second aspect of the first aspect of theembodiments, the controller is configured to determine the position ofthe autonomous transport vehicle based on a drive wheel having a highestvelocity of the at least two drive wheels when a negative torque isapplied by the at least two drive wheels.

In accordance with the second aspect of the first aspect of theembodiments, the controller is configured with an extended Kalman filterfor filtering spurious data from each of the encoders.

In accordance the second aspect of the first aspect of the embodiments,the autonomous transport vehicle includes at least one line followingsensor configured to sense guide lines on a surface of the storage andretrieval system, the controller being further configured to weight datafrom each of the encoders based on a guide line deviation signalsprovided by the at least one line following sensor.

In accordance the second aspect of the first aspect of the embodiments,wherein the controller is configured to verify a position of theautonomous transport vehicle by detecting one or more datum lines on asurface of the storage and retrieval system.

In accordance with the first aspect of the embodiments, the autonomoustransport vehicle includes at least one releasably lockable casterwheel.

In accordance with a second aspect of the embodiments, an autonomoustransport vehicle for transporting items in a storage and retrievalsystem is provided. The autonomous transport vehicle includes a frame, acontroller, at least two independently driven drive wheels mounted tothe frame and at least one caster wheel mounted to the frame and havinga releasably lockable swivel lock. The controller being configured tolock and unlock the releasably lockable swivel lock during a transportof items through the storage and retrieval system based on apredetermined kinematic state of the autonomous transport vehicle.

In accordance with the second aspect of the embodiments, the controlleris configured to individually drive the independently driven drivewheels based on command logic generated from a determination of thepredetermined kinematic state of the autonomous transport vehicle.

In accordance with the second aspect of the embodiments, the controlleris configured to apply a differential torque to the independently drivendrive wheels for effecting curvilinear travel of the autonomoustransport vehicle.

In accordance with the second aspect of the embodiments, the controlleris configured to maintain the releasably lockable swivel lock in alocked state when a lateral position and yaw angle of the autonomoustransport vehicle are below a predetermined deviation value.

In accordance with the second aspect of the embodiments, the controlleris configured to unlock the releasably lockable swivel locksubstantially during an application of differential torque to theindependently driven drive wheels.

In accordance with a first aspect of the second aspect of theembodiments, the at least one caster wheel includes an actuator, a firstlocking member and a second locking member connected to a wheel of theat least one releasably lockable caster wheel, the actuator beingconfigured for a pulse release of the first locking member from thesecond locking member for unlocking the releasably lockable swivel lock.

In accordance with the first aspect of the second aspect of theembodiments, the at least one caster wheel is configured such that thefirst locking member and second locking member are substantially alignedduring substantially straight line travel of the autonomous transportvehicle and the first locking member is biased to automatically engagethe second locking member for locking the releasably lockable swivellock.

In accordance with the first aspect of the second aspect of theembodiments, wherein the autonomous transport vehicle has a longitudinalaxis substantially aligned with the straight line travel of theautonomous transport vehicle and a lateral axis that is transverse tothe longitudinal axis, the first locking member being configured toengage the second locking member in a lateral direction.

In accordance with a third aspect of the embodiments, an autonomoustransport vehicle is provided. The autonomous transport vehicle includesat least two independently driven drive wheels, at least one releasablylockable caster wheel and a controller. The controller includes a stateestimator configured to estimate a kinematic state of the autonomoustransport vehicle wherein the controller issues control commands to theat least two independently driven drive wheels and the at least onereleasably lockable casters based on the estimated kinematic state ofthe autonomous transport vehicle.

In accordance with the third aspect of the embodiments, the controlleris configured to estimate a state of the autonomous transport vehiclebased on data obtained from one or more sensors of the autonomoustransport vehicle.

In accordance with a fourth aspect of the embodiments an autonomoustransport vehicle for transporting items in a storage and retrievalsystem is provided. The autonomous transport vehicle includes acontroller, at least one wheel encoder in communication with thecontroller and at least one line following sensor in communication withthe controller and configured to detect guide lines disposed on a deckof the storage and retrieval system. The controller being configured toestimate a position of the autonomous transport vehicle within thestorage and retrieval system using an extended Kalman filter and sensordata from the at least one wheel encoder. The controller is furtherconfigured to update the extended Kalman filter using sensor data fromthe at least one line following sensor so that an accuracy of theestimated position of the autonomous transport vehicle increases overprevious estimated position determinations.

In accordance with a fifth aspect of the embodiments an autonomoustransport vehicle for transporting items in a storage and retrievalsystem is provided. The autonomous transport vehicle including acontroller, a frame, at least two driven wheels mounted to the frame anda wheel encoder for each of the driven wheels in communication with thecontroller and configured to detect rotation of a respective drivenwheel. The controller being configured to determine a position of theautonomous transport vehicle within the storage and retrieval systemfrom sensor data from an encoder for a driven wheel having the bestwheel odometry of the at least two driven wheels.

It should be understood that the embodiments disclosed herein can beused individually or in any suitable combination thereof. It should alsobe understood that the foregoing description is only illustrative of theembodiments. Various alternatives and modifications can be devised bythose skilled in the art without departing from the embodiments.Accordingly, the present embodiments are intended to embrace all suchalternatives, modifications and variances that fall within the scope ofthe appended claims.

What is claimed is:
 1. An autonomous transport vehicle for transportingitems in a storage and retrieval system, the autonomous transportvehicle comprising: at least two drive wheels, each drive wheel beingindependently driven; a drive wheel encoder disposed adjacent each drivewheel; and a controller in communication with the encoders configured toidentify a kinematic state of the autonomous transport vehicle withinthe storage and retrieval system based only on incremental data from thedrive wheel encoders, received from each encoder, and independent ofdrive wheel slippage.
 2. The autonomous transport vehicle of claim 1,wherein the controller is configured to determine command logic foroperating the autonomous transport vehicle based on the kinematic state.3. The autonomous transport vehicle of claim 1, wherein the autonomoustransport vehicle includes one or more of a wheel encoder for each drivewheel, an inertial sensor, at least one storage slat sensor and at leastone line following sensor, wherein the controller is configured toreceive data from the one or more of the wheel encoder for each drivewheel, the inertial sensor, the at least one storage slat sensor and theat least one line following sensor for identifying the kinematic state.4. The autonomous transport vehicle of claim 1, wherein the controlleris further configured to determine a position of the autonomoustransport vehicle within the storage and retrieval system independent ofdrive wheel slippage.
 5. The autonomous transport vehicle of claim 4,wherein the controller is configured to determine the position of theautonomous transport vehicle based on a drive wheel having a lowestvelocity of the at least two drive wheels when a positive torque isapplied by the at least two drive wheels.
 6. The autonomous transportvehicle of claim 4, wherein the controller is configured to determinethe position of the autonomous transport vehicle based on a drive wheelhaving a highest velocity of the at least two drive wheels when anegative torque is applied by the at least two drive wheels.
 7. Theautonomous transport vehicle of claim 4, wherein the controller isconfigured with an extended Kalman filter for filtering spurious datafrom each of the encoders.
 8. The autonomous transport vehicle of claim4, wherein the autonomous transport vehicle includes at least one linefollowing sensor configured to sense guide lines on a surface of thestorage and retrieval system, the controller being further configured toweight data from each of the encoders based on a guide line deviationsignals provided by the at least one line following sensor.
 9. Theautonomous transport vehicle of claim 4, wherein the controller isconfigured to verify a position of the autonomous transport vehicle bydetecting one or more datum lines on a surface of the storage andretrieval system.
 10. The autonomous transport vehicle of claim 1,wherein the autonomous transport vehicle includes at least onereleasably lockable caster wheel.
 11. A storage and retrieval systemcomprising: at least one autonomous transport vehicle including at leasttwo drive wheels, each drive wheel being independently driven; a drivewheel encoder disposed adjacent each drive wheel; a controller incommunication with the drive wheel encoders of the at least oneautonomous transport vehicle and being configured to identify akinematic state of the at least one autonomous transport vehicle withinthe storage and retrieval system based only on incremental data from thedrive wheel encoders, received from each encoder, and independent ofdrive wheel slippage; wherein the controller periodically verifies thekinematic state along a travel path of the at least one autonomoustransport vehicle wherein the period of verification is based ondetection of a position datum having a predetermined position relativeto a surface being traversed by the at least one autonomous transportvehicle.
 12. The storage and retrieval system of claim 11, wherein thecontroller is configured to determine command logic for operating the atleast one autonomous transport vehicle based on the kinematic state. 13.The storage and retrieval system of claim 11, wherein the at least oneautonomous transport vehicle includes one or more of a wheel encoder foreach drive wheel, an inertial sensor, at least one storage slat sensorand at least one line following sensor, wherein the controller isconfigured to receive data from the one or more of the wheel encoder foreach drive wheel, the inertial sensor, the at least one storage slatsensor and the at least one line following sensor for verifying thekinematic state.
 14. The storage and retrieval system of claim 11,wherein the controller is further configured to determine a position ofthe at least one autonomous transport vehicle within the storage andretrieval system independent of drive wheel slippage.
 15. The storageand retrieval system of claim 14, wherein the controller is configuredto determine the position of the at least one autonomous transportvehicle based on a drive wheel having a lowest velocity of the at leasttwo drive wheels when a positive torque is applied by the at least twodrive wheels.
 16. The storage and retrieval system of claim 14, whereinthe controller is configured to determine the position of the at leastone autonomous transport vehicle based on a drive wheel having a highestvelocity of the at least two drive wheels when a negative torque isapplied by the at least two drive wheels.
 17. The storage and retrievalsystem of claim 14, wherein the controller is configured with anextended Kalman filter for filtering spurious data from each of theencoders.
 18. The storage and retrieval system of claim 14, wherein theat least one autonomous transport vehicle includes at least one linefollowing sensor configured to sense guide lines on a surface of thestorage and retrieval system, the controller being further configured toweight data from each of the encoders based on a guide line deviationsignals provided by the at least one line following sensor.
 19. Thestorage and retrieval system of claim 14, wherein the controller isconfigured to verify a position of the at least one autonomous transportvehicle by detecting one or more datum lines on a surface of the storageand retrieval system.
 20. The storage and retrieval system of claim 14,wherein the at least one autonomous transport vehicle includes at leastone releasably lockable caster wheel.
 21. A method for controlling anautonomous transport vehicle within a storage and retrieval systemcomprising: receiving incremental data from at least two drive wheelencoders, each drive wheel encoder being disposed adjacent acorresponding one of at least two drive wheels of the autonomoustransport vehicle; identifying a kinematic state of the autonomoustransport vehicle within the storage and retrieval system based only onincremental data from the at least two drive wheel encoders independentof drive wheel slippage; and periodically verifying the kinematic statealong a travel path of the autonomous transport vehicle wherein theperiod of verification is based on detection of a position datum havinga predetermined position relative to a surface being traversed by theautonomous transport vehicle; and determining a command logic foroperating the autonomous transport vehicle based on the kinematic state;and issuing the command.
 22. The method of claim 21, wherein verifyingthe kinematic state of the autonomous transport vehicle is further basedon data from each of the at least two wheel encoders for each drivewheel, an inertial sensor, at least one storage slat sensor and at leastone line following sensor.
 23. The method of claim 21, furthercomprising determining a position of the autonomous transport vehiclewithin the storage and retrieval system independent of drive wheelslippage.
 24. The method of claim 23, further comprising determining theposition of the autonomous transport vehicle based on a drive wheelhaving a lowest velocity of the at least two drive wheels when apositive torque is applied by the at least two drive wheels.
 25. Themethod of claim 23, further comprising determining the position of theautonomous transport vehicle based on a drive wheel having a highestvelocity of the at least two drive wheels when a negative torque isapplied by the at least two drive wheels.
 26. The method of claim 23,further comprising filtering spurious data from each of the at least twowheel encoders with an extended Kalman filter.
 27. The method of claim23, further comprising sensing a guide line on a surface of the storageand retrieval system with the at least one line following sensor andweighting data from each of the at least two wheel encoders based onguide line deviation signals provided by the at least one line followingsensor.
 28. The method of claim 27, further comprising verifying theposition of the autonomous transport vehicle by detecting one or moredatum lines on the surface of the storage and retrieval system.